1. Field of the Invention
The present invention relates to an apparatus and a method for dehumidifying and drying resin pellets by removing moisture adhering to and bound water contained in non-crystallized resin pellets or crystallized resin pellets to be used as molding raw material in a resin molding machine.
2. Description of the Related Art
Dehumidifying and drying apparatus of the type under consideration include one disclosed in JP/3233419B2. The apparatus disclosed in the above-cited Patent Document is adapted to heat the resin pellets fed into a drying hopper under reduced pressure and dehumidifies and dries moisture adhering to and bound water contained in them. Such a resin dehumidifying and drying apparatus is effective for dehumidifying and drying crystallized resin pellets. However, problems arise when non-crystallized resin pellets such as polyester type resin pellets are dehumidified and dried under the conditions similar to those for dehumidifying and drying crystallized resin pellets. More specifically, non-crystallized resin pellets are softened and become molten under such conditions.
When resin pellets are softened, they adhere to each other to form resin blocks. Then, it is no longer possible to dehumidifying and drying resin pellets as so many units. Resin blocks produced as resin pellets adhere to each other to form resin blocks can no longer be used as molding raw material without processing them. Additionally, molten resin pellets adhere to the inner surface of the hopper and the surfaces of agitator blades in the hopper for agitating resin pellets to produce blocks. Then, it is no longer possible to dehumidifying and drying them. Furthermore, the resin adhering to the outer surface of the hopper and the surfaces of the agitator blades operates as thermal insulator to make it difficult to efficiently heat resin pellets.
Particularly, non-crystallized resin pellets are apt to be molten and become fused to form resin blocks when heated rapidly.
JP2005/28683A1 proposes a drying apparatus designed to dissolve the above disadvantages. A drying apparatus according to the above-cited patent document comprises a crystallizing hopper for crystallizing granular resin and a drying hopper for drying the resin crystallized in the crystallizing hopper and a hollow rotary shaft that has an open lower end and is treated for thermal insulation is vertically arranged in the crystallizing hopper and provided on the outer surface with agitator wings. The rotary shaft is driven to rotate and hot air is supplied into the crystallizing hopper by way of the rotary shaft.
However, the proposed drying apparatus requires a crystallizing hopper for crystallizing non-crystallized resin pellets and a drying hopper for drying crystallized resin pellets and is dedicated to drying crystallized resin pellets. Thus, the apparatus has large dimensions and is costly.